Converter Lens Aberration Control via Segmented Refractive Groups
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Solution Overview
Problem
Rear converter lenses face challenges in achieving high optical performance and compact size when used with master lenses having short back focal distances, as they struggle to correct field curvature and magnification chromatic aberration due to increased lens diameter and refractive power requirements.
Innovation Solution
A converter lens design with a negative refractive power, comprising a front group with maximum positive refractive power and a rear group, satisfying specific conditional expressions to control refractive power distribution and lens configuration, ensuring the converter lens is small in size and effective in correcting aberrations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the converter lens is disposed at a position where the height of a principal ray of off-axis light rays output from the master lens is relatively high, then the converter lens can be used with a master lens having a short back focal distance, but the diameter of the lens group disposed on the image side in the converter lens increases and field curvature and magnification chromatic aberration become difficult to correct
Solution Approach 1:
The converter lens is divided into multiple lens groups (first lens group with positive refractive power, second lens group with negative refractive power, third lens group with positive refractive power) to independently control aberrations. Each group can be optimized for specific functions: the first group controls field curvature, the second group controls magnification chromatic aberration, and the third group balances the overall system.
Solution Approach 2:
Different regions of the converter lens are assigned different refractive powers and characteristics. The first lens group has higher positive refractive power to address field curvature at the object side, while the second lens group has negative refractive power to correct magnification chromatic aberration at the image side, creating localized optimization throughout the optical path.
2Object-affected harmful factors
If the refractive power of the lens group disposed on the object side in the converter lens is increased, then field curvature can be corrected, but the diameter of the lens group disposed on the image side increases
Solution Approach 1:
The correction of field curvature is divided between multiple lens groups rather than relying on a single high-power lens. The first lens group provides positive refractive power for field curvature correction, while the second and third lens groups with negative refractive power compensate for the resulting increase in image-side lens diameter, achieving a balanced design.
3Object-affected harmful factors
If the converter lens includes more lenses to correct aberrations, then optical performance improves, but the size and complexity of the converter lens increases
Solution Approach 1:
Each lens group is designed with specific refractive power characteristics tailored to its position and function in the optical system. The first lens group has higher positive refractive power for field curvature correction, while the second and third lens groups have negative refractive power for aberration balancing, ensuring each element contributes maximally to overall performance.
Solution Approach 2:
The refractive powers of the lens groups are carefully balanced according to specific conditions: the first lens group has positive refractive power with specific constraints, the second lens group has negative refractive power, and the third lens group has positive refractive power. This parameter optimization ensures effective aberration correction while controlling the total number of lenses required.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The design achieves high optical performance by controlling field curvature, astigmatism, and magnification chromatic aberration while maintaining a compact size, suitable for use with mirrorless cameras and lenses having short back focal distances.
Implementation Method 1
a converter lens that has a negative refractive power as a whole and is disposed on an image side of a master lens so that a focal length of an entire system becomes longer than a focal length of the master lens alone
Data Source
AI summary
A converter lens according to an exemplary embodiment of the present invention is a converter lens that has a negative refractive power and increases a focal length of an entire system. The converter lens includes a front group having a positive refractive power and a rear group having a negative refractive power, and the front group is a lens unit having a combined refractive power having a maximum positive refractive power in a case where the combined refractive power is obtained by combining a refractive power of each lens in order from the lens closest to an object toward an image side. At this time, a focal length of the front group, a focal length of the converter lens, and a lateral magnification of the converter lens when the converter lens is disposed on an image side of a master lens are determined as appropriate.